A typical type scroll compressor comprises orbiting and non-orbiting scroll members having interfitting spiral vanes, the flanks of the vane on one member being in sealing contact with the flanks of the vane on the other member. The vanes define fluid-containing pockets which change in volume as one scroll member orbits with respect to the other scroll member.
Orbital movement of the orbiting scroll is generally provided by an elongated axial crankshaft journaled for rotation in at least one bearing of the compressor. One end of the crankshaft typically has an eccentric crank pin mounted in a hub on the orbiting scroll member, whereby rotation of the crankshaft causes the orbiting scroll member to orbit with respect to the non-orbiting scroll member. In a radially compliant driving arrangement, an unloader bushing may be provided between the crank pin and the drive bearing located in the hub on the orbiting scroll. The crank pin is normally provided with a flat surface for drivingly engaging a corresponding flat surface located on the unloader bushing. The design of the crank pin and the unloader bushing are such that the two flat surfaces provide for a limited amount of sliding motion and thus radial compliance between the crank pin and the unloader bushing. This limited sliding motion permits radial movement of the orbiting scroll with respect to the crank pin and thus unloading of the scroll machine. The angle the flat driving surface on the crank pin may be chosen so that a slight centrifugal force component is introduced to the orbiting scroll by the driving of the crank pin in order to enhance flank sealing. During operation of the compressor, the radial compliancy is advantageous for various reasons, including permitting deflection or the orbiting scroll when debris or liquid coolant are encountered in the compression process and the aiding in the elimination of reverse rotation of the scroll compressor at stop by creating a gap between the non-orbiting and orbiting scroll vanes to release the high pressure gas from the central volume and high pressure pockets of the compressor. This unloading of the scroll machine releases the high pressure gasses to the suction area of the compressor.
As compressor loading increases, due to compressed gas forces, the forces on the two flat driving surfaces can become excessive such that it becomes difficult to insure continuous radial sliding movement between the unloader bushing and the crank pin. In order to prevent damaging wear and/or excessive noise and vibration, the interfacing flat surfaces of the crank pin and the unloader bushing require tight control of both the dimensions and the surface finish requirements of the two surfaces. In addition, lubrication of the two surfaces is a necessity in order to lower the coefficient of friction between the two surfaces and thus the load required for sliding movement between the two surfaces. As the compressor loading increases, the lubrication between the two flat surfaces thus becomes more difficult.
It is therefore a primary objective of the present invention to provide a driving arrangement which obviates the aforesaid problems which can occur under high load conditions, thereby increasing unloader reliability and overall performance.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.